Pressure actuated switch



Dec. 10, 1957 B. H. cLAsoN 2,816,189

\ PRESSURE ACTUATED SWITCH Filed March 16, 1955 7 QQ l United States Patent PRESSURE ACTUATED SWITCH Berti! H. Clason, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Deiaware Application March 16, 1955, Serial No. 494,615

6 Claims. (Cl. 200-'--83) This invention relates to pressure actuated electrical switches and more particularly to the differential type which is adapted to interrupt the continuity of an electrical circuit at one value of pressure and to complete the continuity at a different value of pressure.

This type of switch finds numerous application in the indication or control of a condition of a fluid pressure or related system. A specific example for which the present invention is especially well suited is the control of the compressor of an automotive refrigerating system. In such use it is desirable to provide a simple and inexpensive control switch to start the compressor in response to a low value of pressure and to shut down the compressor at a relatively high value of pressure. For automotive use, the switch must be of rugged construction, insensitive to wide variations of ambient conditions, and must be reliable in operation.

Accordingly, it is an object of this invention to provide a pressure actuated switch of simple construction which is responsive at one value of pressure to interrupt an electrical circuit and responsive at a different value of pressure to complete the electrical circuit.

It is an additional object of this invention to provide a pressure actuated diiferential switch which is of rugged construction, reliable in operation, and economical to manufacture.

Another object is to provide a pressure actuated switch which utilizes a diaphragm and a movable contact member operatively connected through a lost motion connection to provide for differential operation.

In the attainment of these objects, an actuating means and a movable contact adapted for movement to and from engagement with a fixed contact are interconnected by a lost motion connection. The actuating means is operatively connected for displacement by a condition responsive' means, such as a distendable diaphragm. The movable contact may be frictionally constrained against motion and the operating parts may be sealed within a protective housing.

A more complete understanding of the manner in which the invention is carried into effect may be had from the detailed description which follows taken with the accompanying drawings, in which:

Figure 1 is a sectional view of the inventive pressure actuated switch with the switch parts in one condition.

Figure 2 is a cross sectional view taken on line 22 of Figure 1.

Figure 3 is a fragmentary View of the inventive switch with the switch parts in another condition.

Figure 4 is a perspective view showing, in detail, one member of the inventive switch.

Referring now to the drawings there is shown an illustrative embodiment of the invention in a diaphragm type pressure actuated switch. The switch comprises a casing member or metal shell which includes an axially extending conduit 11 terminating in a threaded portion 12 and an opening 13 for the admission of fluid pressure. The conduit 11 of the casing 10 extends into the radial flange 14 terminating in an axially extending flange 16. A pressure responsive diaphragm 17, of any suitable material such as neoprene, is seated against flange 14 in sealing relation therewith to define a pressure chamber 18. A plate member 19, preferably of metallic construction, constitutes a fixed electrical contact and is disposed adjacent the diaphragm 17. Plate member 19 is provided at its central portion with an axially extending annular flange 20 defining a central opening 21. The plate 19 is provided with an axial flange 22 which engages the flange 16 of metal shell 10.

An insulating support or casing member 23, suitably a molded body of thermosetting phenolic plastic, defines a recess or switch cavity 24 to accommodate certain parts of the switch structure, to be described subsequently. The support member 23 is seated against the plate 19 and is provided with a radial shoulder 25. The axial flanges 16 and 22 of the casing 10 and plate 19, respectively, are crimped over the shoulder 25 to retain these parts in assembled relation and to compress the periphery of the diaphragm 17 between the plate 19 and the radial flange 14 to provide a fluid tight seal. Thus, the casing member 10 and easing member 23 provide a two-part housing including a pressure chamber 18 and a switch cavity 24 separated by transverse diaphragm 17.

A terminal post 26 adapted to be connected in an external electrical circuit (not shown) extends through the support member 23 terminating in the cavity 24 and is securely retained in position by the knurled portion 27 and the undercut portions 28. Actuating means or piston 29, of conductive material such as brass and preferably cylindrical in cross section, is slidably disposed within the cavity 24. The actuating means is provided with a transverse slot 30 defined by axially spaced shoulders 31 and 32. A boss 33 is provided on actuating means 29 to retain an insulating member or bearing member 34 in alignment with central opening 21 for engaging the diaphragm 17. Resilient means such as electrically conductive helical spring 36 is seated against a shoulder 35 in the support member 23 and engages the terminal post 26 at one end and engages the actuating means 29 at the other end providing electrical continuity therebetween. The spring 36 urges the actuating means 29 and bearing member 23 toward engagement with the diaphragm 17 A movable contact member 37, adapted to be moved to and from engagement with fixed contact plate 19, is of generally U-shape configuration having a base portion 38 and a pair of contact leg portions 40 and 40. The base portion is disposed in transverse slot 30 and is adapted for limited relative movement between shoulders 31 and 32 to provide a lost motion connection with the actuating means 29. A corrugation or dimple 39 is provided on base portion 38 to insure continuous electrical contact with actuating means 29 during relative axial movement. The contact leg portions 46 and 40 extend axially toward fixed contact plate 19 and are disposed in axial slots 44 and 45 respectively constituting guide means defined by support member 23 at opposite ends of the transverse slot 30. The contact legs 40 and 40 are provided with corrugations or dimples 41 and 41', respectively, to provide frictional engagement of the contact legs with support member 23 and thus afford limited frictional constraint against axial motion of the movable contact 37. Concurrent motion of the movable contact 37 and the actuating means 29 occurs only when the base portion 38 is engaged by shoulder 31 or 32 of actuating means 29.

It will be noted that in the free condition of the switch with only a very low value of pressure, such as atmospheric, in chamber 18 the parts assume the relative position shown in Figure l. The diaphragm 17 is distended away from the plate 19, the extent of which depends upon 9 o the properties of the diaphragm and the spring 36. In normal operation this condition will not obtain because the low value of pressure at which the switch is calibrated to function will be sutficient to maintain the diaphragm 17 in a non-distended condition flat against the plate 19. In this non-distended condition, the position of the actuating means is such that the movable contact is in engagement with the fixed contact 19. The diaphragm 17 must be distended into the confines of opening 21 to cause concurrent motion of actuating means 29 and movable contact 37 to displace the latter from engagement with fixed contact 19. This action occurs under the influence of a relatively high pressure in chamber 18.

In operation, the inventive switch of the illustrative embodiment functions to interrupt the electrical circuit at a high value of pressure in the chamber 18 and to complete the electrical circuit upon a relatively low value of pressure in chamber 18. In Figure l, the switch is shown with the parts in the position assumed with a low value of pressure in the chamber 18 acting upon the diaphragm 17. The force exerted by spring 36 is suflicient to overcome the force exerted by diaphragm 17 and to maintain the shoulder 32 or" actuating means 29 in engagement with the base portion 38 of movable contact 37. Thus, the contact legs 40 and 4t) are in engagement With the fixed contact plate 19. The electrical circuit in this condition i completed from the terminal post 26 through the spring 36, actuating means 29, movable contact 37 and thence through fixed contact plate 19 to casing member 10. Upon an increase of pressure in chamber 18 toward a predetermined high value, the force exerted thereby upon the diaphragm 17 increases until it is sufficient to overcome the force of spring 36 and to urge the diaphragm into close surface engagement with the plate 19 at which position the diaphragm is substantially nondistended. This movement displaces the actuating means 29 a distance less than that required to cause shoulder 31 to engage base portion 38 of movable contact 37. Thus there is no movement of contact 37 and the contact legs 40 and 40' remain in firm engagement with contact plate 19 by virtue of frictional engagement with the support member 23. During this displacement of actuating means 29 continuous engagement of movable contact 37 with actuating means 29 is assured by the corrugation 39 and the continuity of the electrical circuit is uninterrupted. As the pressure continues to increase, the central portion of the diaphragm 17 is distended into the opening 21 in plate 19. The fluid pressure is thus effective through the diaphragm 17 to further displace the actuating means 29 against the resistance of the spring 36. During this portion of travel, shoulder 31 of the actuating means engages the base portion 38 of movable contact 37 and displaces the contact legs 40 and 40' from engagement with contact plate 19. This operating condition with the circuit continuity interrupted is illustrated in Figure 3.

Upon decrease of fluid pressure in chamber 18 toward a predetermined low value, the force exerted by the spring 36 overcomes that exerted by the diaphragm 17 on the actuating means 29 causing displacement thereof toward the diaphragm. In this portion of travel of the actuating means 29, the movable contact 37 is retained in position by its frictional engagement with the support member 23 until the lost motion between contact 37 and actuating means 29 is taken up and shoulder 32 engages the base portion 39. Upon further decrease of the pressure in chamber 18 the actuating means is further displaced toward the diaphragm 17 and the contact legs 40 and 40' engage the fixed contact plate 19. Thus, the circuit continuity is restored at the predetermined low value of pressure in chamber 18.

Although this invention has been described with respect to a particular embodiment, this embodiment i not to be construed in a limiting sense. Many modifications and variations within the spirit and scope of the invention will now occur to those skilled in the art. For a definition of the invention, reference is made to the appended claims.

I claim:

1. A pressure actuated switch comprising a casing and a diaphragm defining a pressure chamber, said casing defining an opening for admitting fluid pressure to one side of said diaphragm, a fixed contact plate disposed adjacent the other side of said diaphragm and defining a central opening, said diaphragm being secured at its periphery between said plate and said casing, a support member secured to said casing, actuating means slidably disposed in said support member in alignment with the opening in said plate, resilient means interposed between said support member and said actuating means for urging the actuating means toward engagement with said dia phragm, a movable contact adapted to be moved to and from engagement with said fixed contact plate, said diaphragm being movable from a first condition in which it is substantially non-distended adjacent said plate to a second condition in which it is distended into the con fines of said central opening under the influence of a high value of fluid pressure in said chamber, and lost motion means connecting said movable contact to said actuating means and being ineffective to cause concurrent motion of said actuating means and said movable contact until said diaphragm is moved to said second condition.

2. A pressure actuated switch comprising a metallic casing and a diaphragm defining a pressure chamber, said casing defining an opening for admitting fluid pressure to one side of said diaphragm, a fixed contact plate disposed on the other side of said diaphragm in peripheral engagement with said metal casing, said contact plate defining a central opening, an insulating support member secured to said casing and defining a switch cavity adjacent said contact plate, a terminal post extending through said support member into said cavity, actuating means having a conductive portion and slidably disposed in said cavity and extending into said central opening, a movable contact adapted to be moved to and from engagement with said contact plate, a conductive spring interposed between said terminal post and said conductive portion urging said actuating means toward engagement with said diaphragm, and a lost motion connection between said movable contact and said actuating means and including means providing continuous electrical continuity between said movable contact and said conductive portion.

3. A condition responsive switch comprising a condition responsive member movable in response to a change in condition, an insulating support member and a fixed contact disposed adjacent said condition responsive member, actuating means slidably disposed in said insulating support member and connected with the condition responsive member, a spring interposed between said insulating support member and said actuating means urging said actuating means toward said condition responsive member, axially spaced shoulders defining a transverse slot in said actuating means, said insulating support member defining an axially extending slot at one end of said transverse slot, and a movable contact member including a base portion disposed in said transverse slot and an axially extending contact leg disposed in said axial slot in frictional contact with the support member and adapted for engagement with said fixed contact.

4. A pressure actuated switch comprising a casing member and a diaphragm defining a pressure chamber, said casing member defining an opening for admission of fluid pressure to one side of said diaphragm, a support member secured to said casing and defining a switch cavity adjacent the other side of said diaphragm, a fixed contact disposed in said cavity, actuating means slidably disposed in said support member, resilient means urging said actuating means towardengagement with said'diaphragm, said actuating means including axially spaced shoulders defining a transverse slot, said support member defining an axially extending slot adjacent each end of said transverse slot, a generally U-shaped movable contact having a base portion disposed in said transverse slot and contact leg portions disposed in respective axially extending slots, said contact leg portions being constrained against motion by frictional engagement with said support member in said axially extending slots whereby concurrent motion of said actuating means and said movable contact occurs only when said base portion is engaged by one of said axially spaced shoulders on said actuating means.

5. A pressure actuated switch comprising a casing member and a diaphragm defining a pressure chamber, said casing member defining an opening for admission of fluid pressure to one side of said diaphragm, a support member secured to said casing and defining a switch cavity adjacent the other side of said diaphragm, a fixed contact plate disposed in said cavity adjacent said diaphragm and defining a central opening, actuating means including a bearing member in alignment with said central opening and slidably disposed in said support member, resilient means urging said actuating means toward said diaphragm, said actuating means including axially spaced shoulders defining a transverse slot, said support member defining an axial slot adjacent each end of said transverse slot, a generally U-shaped movable contact having a base portion and a pair of contact leg portions, said base portions being disposed in said transverse slot and adapted for relative motion between said spaced shoulders, said contact leg portions being disposed in respective axial slots and in frictional engagement with said support member whereby concurrent motion of said actuating means and said movable contact occurs only when said base portion is engaged by one of said axially spaced shoulders on said actuated means.

6. A pressure actuated switch comprising a metallic casing member and a diaphragm defining a pressure chamber, said casing member defining an opening for admission of fluid pressure to one side of said diaphragm, a support member secured to said casing member and defining a switch cavity adjacent the other side of said diaphragm, a fixed contact plate defining a central opening and being disposed in said cavity adjacent said diaphragm and in peripheral engagement with said metallic casing member, a terminal post extending through said support member into said cavity, actuating means including an electrically conductive portion and an insulating bearing portion slidably disposed in said support member with said bearing portion extending into said central opening, a conductive spring interposed between and terminal post and the conductive portion of said actuating means for urging said actuating means toward said diaphragm, said electrically conductive portion including axially spaced shoulders defining a transverse slot, said insulating support member defining an axial slot at each end of said transverse slot, a generally U-shaped movable contact having a base and contact leg portions, said base portion disposed in said transverse slot and including a corrugation to maintain continuous electrical contact with said conductive portion during movement of said base portion between said spaced shoulders, said contact leg portions adapted to be moved to and from engagement with said fixed contact plate and disposed in said axial slots, each of said contact leg portions being provided with a corrugation to provide limited frictional constraint against movement of said movable contact whereby concurrent motion of said actuating means and said movable contact occurs only when said base portion is in engagement with one of said shoulders.

References Cited in the file of this patent UNITED STATES PATENTS 1,951,245 Jardine Mar. 13, 1934 2,200,599 Gaynor May 14, 1940 2,430,428 Katcher Nov. 4, 1947 2,698,887 Shaw Jan. 4, 1955 

